Re: A little OT: Diffie Hellman Exchange and Encryption on Cisco Routers
From: Ranjeet Shetye (ranjeet.shetye2_at_zultys.com)
Date: 08/05/03
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Date: Tue, 5 Aug 2003 10:38:22 -0700 To: 'pen-test' <pen-test@securityfocus.com>
Here's a little note I wrote a long time back, that I keep around to
remind myself of the DH details.
----------------
Alice knows a.
Bob knows b.
They both know g and n, where g has the mathematical property that it
is primitive mod n.
Alice sends A (= g ^ a (mod n)) to Bob
Bob sends B (= g ^ b (mod n)) to Alice.
Alice does kA = B ^ a mod n
Bob does kB = A ^ b mod n = ((g ^ a) mod n) ^ (b mod n) = (g ^ a ^ b)
mod n = ((g ^ b) mod n) ^ (a mod n) = B ^ a mod n = kA
i.e. both Alice and Bob have ended up with the final same number kA ==
kB, without sharing their secrets 'a' or 'b' with each other.
----------------
For a 100-line technical summary of many of the mathematical concepts
used in cryptography, here's a link. chew on it slowly :)
http://archives.neohapsis.com/archives/cisspstudy/2001-q4/0131.html
HTH,
-- Ranjeet Shetye Senior Software Engineer Zultys Technologies Ranjeet dot Shetye2 at Zultys dot com http://www.zultys.com/ -- The views, opinions, and judgements expressed in this message are solely those of the author. The message contents have not been reviewed or approved by Zultys. --------------------------------------------------------------------------- ----------------------------------------------------------------------------
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